Subsea field development and completion wells are often drilled in a pattern that spaces the wells apart from each other. Some wells have production trees that connect to flowlines at the sea floor. The flowlines typically lead to manifolds, templates, or other subsea processing units that collect or re-distribute the product coming from the well. The flowline connector for each tree is often configured horizontally and off to one side of the tree.
When developing the field, the operator orients the tree connector to align with a flowline hub or receptacle. That hub or receptacle may reside in a multi-well template that includes manifold components, in which the template will therefore receive a Christmas or production tree.
A typical subsea wellhead structure has a high pressure wellhead housing secured to a low pressure housing, such as conductor casing. The wellhead structure supports casing that extends into the well. One or more casing hangers land in a component of the wellhead structure, such as the high pressure wellhead housing, with each casing hanger being located at the upper end of a string of casing that extends into the well. A string of tubing extends through the casing for conveying production fluids, in which the tubing string is supported using a tubing hanger. The area between the tubing and casing is referred to as the annulus. Vertical completion arrangements typically plan for the tubing hanger to be landed in and supported by the wellhead structure. In this type of completion arrangement, the Christmas or production tree may attach to the wellhead structure, such as the high pressure housing, tubing spool, tubing head, or wellhead adapter, for controlling the well fluid. The tubing hanger landed in the wellhead structure will have one or more passages that may include a production passage, an annulus passage, and various hydraulic and electric control lines. While allowing access to the annulus passage, having more than one passage might lead to accurate tree to tubing hanger orientation. The tree has isolation tubes that stab vertically into engagement with the passages in the tubing hanger when the tree lands on the wellhead structure. These vertical connections may lead to precise alignment of the tree with the tubing hanger both in the vertical and the radial orientation.
Because the tree may be aligned to the tubing hanger and the flowline connection, the tubing hanger may then be aligned to the flowline connection when landed. In this type of completion arrangement, orientation is typically achieved by using the blowout preventer (BOP) assembly for guidance. The BOP assembly has an orientation pin within it that can be extended into the bore. The tubing hanger has an orientation member located in the running string that engages the internal orientation pin of the BOP assembly, and therefore aligns the tubing hanger. The BOP assembly and the tree assembly then each have an external alignment receptacle that fits over a post or feature outside the wellhead structure that is oriented to the flowline heading.
Accordingly, over the last thirty years, the search for oil and gas offshore has progressively moved into a wider range of accessible environments. As such, it remains a priority to increase the reliability of such systems to be free of installation issues.